The production of linear copolymers of alternating carbon monoxide and ethylene [poly(ethylene-alt-carbon monoxide) referred to as PEACO], or other copolymers of ethylene and one or more unsaturated organic compounds via catalysts in a slurry reaction system employing a polar diluent such as methanol, chloroform, methylene chloride, or acetone, or a mixture of these or other similar diluents is seriously hampered by reactor fouling. The polymer produced coats the walls, cooling coils, stirrer, thermocouples, and other internal structures of the reactor. See, for example, the discussion of this problem in European Patent Application 0 404 228. Removal of this coating is laborious and requires the use of a die grinder and wire brushes. After a three hour polymerization run, it can take over two hours to clean the reactor. Part of the polymer produced in this manner is unusable as it is highly discolored and not granular. The purity and the bulk properties of the polymer may be adversely affected by such material. The polymer also has an irregular morphology. Further, samples removed from the reactor contain clumps and do not flow well.
A catalyst which would reduce reactor fouling is highly desirable. If reactor fouling is reduced, increases in reactor operability would result. The elimination of reactor fouling is especially important in a continuous production unit.
A catalyst which does not require a polar diluent in the reactor, but can produce PEACO in either polar or non-polar diluents, would be an additional improvement since this would broaden the flexibility of the process. Also, non-polar diluents, e.g., hexane or heptane, would be less likely to swell the polymer hence contamination of the polymer by components of the catalyst system would be less likely. This would be reflected in a higher level of polymer purity and alleviate the need for costly post-reactor operations to remove contaminants from the resin.
Supported catalysts would also allow the polymer to be produced in a gas phase reaction system. Crucial to this, is the ability of the supported catalyst to control the morphology of the produced polymer particle. The catalyst should yield a polymer particle with properties, such as bulk density and sphericity, within a range which will allow for fluidization. The control of these properties leads to improvements in the handling characteristics of the polymer such as its flowability.
Supported catalysts are described in the prior art of PEACO production. U.S. Pat. No. 4,778,876 discloses a process for producing PEACO using catalyst solutions supported on organic or inorganic carrier materials including polymers such as PEACO itself. The patent teaches that polymers of higher molecular weight will result when hydrogen is present in the reactor during polymerization than when it is absent. Lower molecular weight polymers are achieved by raising the temperature of the polymerization. A supported catalyst which produces lower molecular weight polymers in the presence of hydrogen is not disclosed. Furthermore, the use of hydrogen as a chain transfer agent would allow one to obtain relatively lower molecular weight polymers without having to run polymerizations at elevated temperatures.
Supported catalysts are also described in European patent application 0 404 228. The production of these catalysts requires the synthesis of ligands with pendant reactive groups which can react with suitable functionalized supports prior to metallation under the appropriate reaction conditions. A supported catalyst which would not require exotic ligands and which was less complex to prepare would lower the cost of producing PEACO with supported catalyst systems.
The metallic components of these catalyst systems are relatively expensive. Therefore, finding means to maximize the metal normalized activity of the catalyst is highly desirable. Since operating costs increase as the pressure requirements of a reactor system increase, it would be beneficial to find ways of achieving acceptable catalyst activities at the lowest possible reaction pressures. Materials which, when present in the reaction zone, increase the activity of the catalyst allowing reaction pressures to be lowered would be of significant value to a catalytic PEACO production process.